To improve the thermodynamic properties of internal combustion engines, mechanical devices that influence the working cycle of the valve drive and make it possible, for example, to vary, as a function of speed, the opening times or the stroke of the gas exchange valves of cylinders of the internal combustion engine are known.
A valve drive of the initially mentioned type, in which a cam support is arranged in a rotationally fixed and axially movable manner on a basic camshaft, is already known from DE 10 2004 011 586 A1. To actuate two gas exchange valves of a cylinder of the internal combustion engine, two axially offset cam groups, each of which has two cams with different cam profiles, are provided on the cam support. By axial shifting of the cam support on the basic camshaft between two shift positions, in each case one of the two cams of each cam group can be brought into mechanical contact with a cam follower of one of the gas exchange valves, as a result of which the stroke and/or the opening times of the gas exchange valve can be adjusted. The axial shift of the cam support on the camshaft is carried out using two worm drives, which are arranged at an axial distance from one another in the cylinder head housing of the internal combustion engine, whereby each worm drive has a final control element in the form of an actuator and an engagement element in the form of a driving pin, whereby the latter can be caused to engage by actuating the final control element with a curved link on the cam support. In one of the two worm drives, the curved link has a left-twist helical groove and in the other of the two worm drives, it has a right-twist helical groove, so that the cam support is shifted right or left, depending on whether the adjusting element of one or the other worm drive is actuated. The cam support can be rotated and axially shifted in a stationary bearing between the two cam profile groups. EP 1 608 849 B1 also discloses such a valve drive.
To improve the influence of the working cycle of the valve drive, it would be desirable to expand the cam groups by another cam with another cam contour or another cam profile. Such an expansion of the cam groups by another cam or another cam profile necessitates, however, to move the cam support back and forth between three different shift positions in which in each case, another cam or another cam profile works together with the cam follower. As a result, the movement path of the cam support is longer, which, in view of the relatively small axial distance between two adjacent gas exchange valves of a cylinder especially in the case of a mounting of the cam support between the valves, can lead to problems in the axial dimensioning of the bearing.
Based on this, the object of the invention is to improve a valve drive of the initially mentioned type to the extent that the movement path of the cam support can be readily increased with respect to the axial dimensioning of the bearing, in particular when the latter is arranged between the valves.